Thieves were one of the available factions-for-hire during the Renaissance, alongside courtesans, mercenaries and the Romani. They were adept free-runners, and possessed a number of guilds in different cities; several of these, including the Venetian and Roman guilds, were allied to the Assassin Order. As such, they possessed a measure of virtue, in that they refused to steal from the poor and fought to defy the local, corrupt nobility.
In regards to leadership, the Florentine, and later the Roman guild was led by La Volpe, and the Venetian guild of thieves was managed by Antonio de Magianis.
However, a number of thieves were independent of the Order. In particular, the Cento Occhi were allied to the House of Borgia, and sought to counteract the Assassins; unaffiliated pickpockets chose to steal freely as well.